1. Field of the Invention
The present invention relates to a method and apparatus for controlling the motion of a head relative to a magnetic or other disk shaped recording medium.
2. Description of the Prior Art
A head such as a magnetic head or an optical pickup is moved toward a target track of a disk shaped recording medium such as a magnetic disk or an optical disk so as to position the head on the target tack. When the head is moved, the speed of the head is controlled in accordance with a speed profile (speed reference) until it approaches the target track. When the head approaches the target track, it is positioned on the target track by means of a position control. The speed profile which refers to the basis of the speed control is determined by a distance x between the present position of the head and the position of the target track.
For example, in the case of a uniform deceleration, the following equations can be satisfied. EQU v=at EQU x=1/2at.sup.2
where v: speed, a: deceleration, t: time, x: distance. Thus, when t is removed from the above equations, the speed profile, which is the function representing the relationship between the speed v and the distance x, can be expressed as (v=.sqroot.2ax).
Since it is difficult to obtain the above mentioned speed profile by software calculations, conventionally it is stored as a table in memory. Depending on the distance x, the speed v is read from the memory. When data is discretely input as for a sector servo, the unit of the data in the table is the distance moved at sampling intervals. In the case where pulses representing motion through the centers of tracks are counted, the unit of the data is one track.
Recently, in order to increase the storage capacity of the disk, the pitches of the tracks therein are made narrow. For example, in a 3.5 inch hard disk, the number of tracks exceeds 1500. Thus, it is expected that the TPI (tracks per inch) will increase.
When the speed profile table has a track unit resolution, it is necessary to provide data for each of a large number of tracks thereby increasing the required memory capacity for storing the table.
On the other hand, when the head speed becomes fast, a speed profile with much higher accuracy than the above mentioned method is required. Thus, in the vicinity of the target track, the speed should be controlled with a resolution of for example 1/2 of a track. However, when the resolution is increased, the required memory capacity of the data table for the speed profile is further increased.